With my new Ultra 120 Extreme and Scythe fan I'm able to run my Q6600 at 3.6GHz. I'm using 9x400 with the ram locked at 1000MHz and my vcore set to 1.4 in the BIOS. Seems stable so far. I've not had any problems in games or applications so far. I ran prime95 for a few minutes just to see what the max load temps were and core0 (the hottest one) would hover around 64-65. The CPU idles around 45C on core0.

Using the stock HSF core0 idled around 42C at stock speeds so I'm very happy with this HSF combo. I'm guessing the temperature difference between the cores is a result one of any combination of 1) uneven compound spread 2) uneven spreader surface 3) uneven HS surface. Core0 is always the hottest and core1 is usually about 2-5C cooler than core0. Cores2 and 3 are sometimes almost 10C cooler than the others. Any additional thoughts on that?